The invention relates to a circulation evaporator for separating mixtures of more volatile and less volatile components, which comprises a discharge container containing at least two chambers. The invention further relates to a process for the separation by distillation of a mixture consisting of a more volatile and a less volatile components.
Circulation evaporators according to the state of the art generally contain an evaporator and a discharge container connected via a connecting piece to said evaporator, a condenser, a vacuum pump, a recirculating line, which connects the discharge container to the evaporator and contains a circulation pump, a feed line for the raw mixture and an outflow line for the purified mixture. The outflow of the purified mixture in this case is generally undertaken from the discharge container; the feed of the raw mixture is generally undertaken into the recirculating line, through which the mixture is pumped from the discharge container to the evaporator. A circulation evaporator according to the state of the art is represented in FIG. 1.
Typical examples of circulation evaporators according to the state of the art are described, for example, in Dr Hermann Stage, Fettsxc3xa4ure-Geradeausdestillation und-Fraktionierung unter dem Gesichtswinkel der Wirtschaftlichkeit, CZ-Chemie-Technik, Annual Set 2, pages 254-260 [1973]; Joachim Gebel, Gxc3xclle-Aufbereitung: umweltgerecht und wirtschaftlich, WLB, Wasser, Luft und Boden 6, pages 20-26 [1992]; B. Gericke, Zwangsumlaufverdampfer im GUD-Prozexcex2 und Druckaufgeladenen Systemen, Part 1: Atmosphxc3xa4rischer GUD-Verdampfer, Brennst.-Wxc3xa4rme-Kraft, Vol. 4, No. 6, pages 247-256 [1992] and B. Gericke, Zwangsumlaufverdampfer im GUD-Prozexcex2 und in druckaufgeladenen Systemen, Part 2: Druckaufgeladener Kohlegas-Verdampfer, Brennst.-Wxc3xa4rme-Kraft, Vol. 44, No. 7/8, pages 295-304 [1992].
If circulation evaporators are used for separating lacquer-resin/isocyanate mixtures, it is necessary to work at quite high temperatures and at low absolute pressures in order to adjust the desired purity of the lacquer resin. In order to avoid excessive temperatures, the circulation evaporators have to make a large evaporation surface available. This results in large items of apparatus and long dwell-times.
In the case of excessive temperatures and excessive residence-times under temperature loading a partial decomposition of the lacquer resin can occur, as well as a change in the color of the lacquer resin, manifesting itself in an increase in the color index.
It is an object of the present invention to provide a circulation evaporator with which the evaporation temperature can be lowered and the thermal load on the mixture consisting of more volatile and less volatile components can be diminished. It is another object of the invention to provide a process for the separation by distillation of a mixture containing more volatile and less volatile components at reduced evaporation temperature.
The invention relates to a circulation evaporator containing
an evaporator and a discharge container connected via a connecting piece to said evaporator,
a condenser,
a vacuum pump,
a recirculating line, which connects the discharge container to the evaporator and contains a pump, a feed line for a raw mixture,
and an outflow line for the purified mixture,
wherein the discharge container contains at least a chamber for the feed and a chamber for the outflow, and
the chamber for the outflow, to which the outflow line for the purified mixture is connected, is directly connected to the connecting piece for the discharge of the unevaporated liquid from the evaporator, and
the chamber for the feed, into which the feed line for the raw mixture leads, is directly connected to the condenser.
The invention will be described in exemplary manner on the basis of the following Figures.